如何在Runnable中更新变量？

Question

I'm trying to create a Runnable that keeps running, but I need to makes changes to a variable from outside, to pause or resume the work that the Runnable is doing.

This is my Runnable implementation:

private boolean active = true;


 public void run() {
    while (true) {
        if (active) { //Need to modify this bool from outside
            //Do Something
        }
    }
}

 public void setActive(boolean newActive){
     this.active = newActive;
 }

In my main class I call:

Thread thread = new Thread(myRunnable);
thread.run();
myRunnable.setActive(false); //This does not work!!! 
                                 //The boolean remains true inside myRunnable.

I've tried with the "volatile" modifier on active, but still it won't update. Any ideas are greatly appreciated.

Answer 1

Thread thread = new Thread(myRunnable);
thread.run();
myRunnable.setActive(false);

The third line will only execute after the run() method has returned. You are executing everything in a single thread, sequentially. The second line should be

thread.start();

And the field should be volatile.

Note, however, that setting the active field to false will make the thread enter a busy loop doing nothing, but consuming CPU by looping constantly. You should rather use a lock to wait until you can resume.